"Trusting the population to take sensible precautions" is the flaw in your argument. We all know a sizeable cohort of the population is not sensible. In an emergency you cannot trust to chance.
As for locking down the healthy to protect the vulnerable that's eminently sensible and it's a highly important defensive measure.
Just because you are dead against lockdowns it doesn't mean, as a last resort, they shouldn't have to be deployed. Comparing Sweden to the UK is fatuous; for a start their population density is much much lower and I seem to recall they admitted themselves they got it wrong because their COVID death rate spiralled in the latter stages of the pandemic.
Unfortunately in times of crisis unpleasant strategies often have to be deployed. Whether or not you dislike those measures is not relevant.